Sega Pico is Sega's toy with hardware similar to Genesis/MegaDrive. Recently some prototype ROMs appeared for it, and I've done some work on emulating them. The result is this little document and this little emulator.

What I have problems with is figuring out what kind of PCM format Pico is using. Some raw samples can be found here, here and here. Also they can be easily extracted from ROMs themselves (they are raw data chunks, copied by game to sound chip when needed). I thought maybe somebody of you tech people want to check these.

EDIT: updated emu link to bugfix release.

Last edited by notaz on Thu May 22, 2008 9:06 pm, edited 1 time in total.

notaz wrote:What I have problems with is figuring out what kind of PCM format Pico is using. Some raw samples can be found here, here and here. Also they can be easily extracted from ROMs themselves (they are raw data chunks, copied by game to sound chip when needed). I thought maybe somebody of you tech people want to check these.

Yes, these samples are 4-bit ADPCM, but I haven't had much time to look at all this so I'll have to check it out later. In any case, way to go!

I think you'll find the PCM chip is the Sega branded 315-5641. It takes all 16 data lines (which according to the memory map the PCM chip does), and it's the only device on that board I can't identify.

Looking at the PCB shots from that link you posted, IPL0 isn't connected. That would limit the autovector interrupts to levels 2, 4, and 6, same as the Mega Drive. If there are handlers in those autovectors, I don't think they could be triggered by an interrupt.

EDIT:
Looking closely at the scans again, it is possible IPL0 is connected under the chip.

Nemesis wrote:I think you'll find the PCM chip is the Sega branded 315-5641. It takes all 16 data lines (which according to the memory map the PCM chip does), and it's the only device on that board I can't identify.

What do you think 315-5639(?) is, then? 315-5640 is the drawing pad controller, it seems.

Nemesis wrote:I've got a query about one thing notaz. How sure are you about the following info:
[...]

I think it's under the chip, because some games don't even boot until IRQ3 happens (they wait for some var which is set in IRQ3 handler).

IC12 and IC13 are not present, but space is provided for them on the board. IC12/IC13 are an alternate VRAM, which would be the same type used in the original Mega Drive. Apparently they designed the board to support both types, probably so they could use whichever was cheaper at the time of manufacture, and they opted for the single IC14 VRAM chip when they manufactured this unit.

notaz wrote:I think it's under the chip, because some games don't even boot until IRQ3 happens (they wait for some var which is set in IRQ3 handler).

I'm concerned that since these ROMs are 'prototype' software that they might be intended to run on 'prototype' hardware? Has anyone gotten any of these prototypes to run on a stock Pico? Perhaps if someone manages to dump a retail Pico cartridge we can get more answers.

Could well be. I wouldn't have a clue from looking at it. I've only listed part names where I'm sure about them though.

Perhaps if someone manages to dump a retail Pico cartridge we can get more answers.

I've got a couple of carts on the way, and we have the pinout. I'm going to try rigging up an adapter to hook it into the Mega Drive, then dump it through MoD's cable. Shouldn't be too hard. There's nothing unusual in the pinout that I can see.

Some Pico carts arrived in the mail yesterday. I was hoping to dump them by cannibalizing a PCI connector and using one side of it to connect to the cart (49 pins per side, compared to 50 on the Pico cart), but the pin spacing is off by a fraction of a millimeter. I'm probably going to have to buy a Pico unit and remove the real connector from that. It'll probably take another week to organize, but it'll be better in the end anyway.